Estimation of Ion Diffusion Coefficients at the Stagnant Layer Using TiO₂Aqueous Suspension Zeta Potential Data

The solid-liquid interface of anatase-water nanofluids has been characterized. Combined data of electrophoretic mobility and conductivity of the colloidal suspensions have been used to evaluate zeta-potentials. Plots of the suspension conductivity as a function of the bulk conductivity are essentially linear, allowing for the establishment of the entire surface conductivity. The main contribution to the surface conductivity stemmed from the counter charge behind the slip plane. Whereas the diffuse layer surface conductivity is generic, the stagnant layer conductivity is system-specific; therefore, evaluation of the later requires insight into such properties as the distribution of charges and lateral mobilities. Based on a simple analytical theory we can also estimate the diffusion coefficient of counterions in the stagnant layer. The results lead to a good agreement between theory and experiment.